1. Field of the Invention
This invention relates to syringes. More specificially, this invention relates to syringes for the administration of small amounts of high viscosity fluids, and in particular, syringes adapted for the delivery of silicone fluids for dermatological purposes.
2. Brief Description of the Prior Art
Syringes adapted for the microadministration of highly viscous liquids, such as silicone fluid, are known in the art. For example, U.S. Pat. No. 3,958,570 discloses hypodermic syringes and syringe capsules which maintain a high pressure between the syringe plunger and barrel. The syringes are constructed so that the interface between the syringe barrel and syringe plunger is resilient and of low friction and so that zero or negative allowance between the barrel and the plunger is maintained. Preferably, the syringe barrel is formed from a resilient plastic such as polypropylene or polyethylene; and the syringe plunger is a rigid rod made of a material such as steel or an engineering plastic such as polyoxymethylene (acetal) resin. The plunger rod is preferably coated with a low friction material, such as a fluorinated hydrocarbon resin, or a silicone resin, or any other similarly low friction, preferably resilient, material. Other types of prior art syringes employ various sealing techniques which are appropriate for low pressure applications, but which are inadequate for high pressure micro applications, in that the prior art barrels tend to crack and/or the syringes tend to develop leaks.
One difficulty encountered with syringes constructed using polypropylene barrels, such as disclosed in U.S. Pat. No. 3,628,523, is that such syringes are reusable only to a limited extent. In order to be able to reuse syringes employed in medical procedures it is necessary to sterilize the syringes before each use. Syringes made using thermoplastic materials having relatively low glass transition temperatures, such as polypropylene, cannot be autoclaved for sterilization. Instead, they must be exposed to a sterilizing gas, such as ethylene oxide. However, even when this precaution is taken to guard against thermally deforming the polypropylene syringe, it has been found that syringes constructed using polypropylene barrels may be reused for only a limited number of times before cracks or leaks develop, or the syringes become otherwise unsuitable for further use.
The present invention provides a remedy to the problem of limited life expectancy encountered with syringes having polypropylene barrels. The present invention provides syringes which may advantageously be reused a multitude of times. The syringes may be sterilized between uses by autoclaving; a sterilizing gas such as ethylene oxide and the associated sterilization equipment are not required.